Rail inspection apparatus



April 7, 1936.

Filed June 20, 1935 Invencqrs: Cramer \ALLaPierre,

Robert F. Edgar;

Thei Attorney.

all

atented P l 1936 lTE STATES 2,036,8l4l RAH lINSPJEC'llON APPARATUS Cranmer W. lLa Pierre and Schenectady,

Robert lF'. Edgar,

N. 2., assignors to General Electrio Company, a corporation of New York 3 Claims.

Our invention relates to magnetic testing dev ces and has for its principal object the provision Other and further objects and advantages will become apparent as the description proceeds.

In accordance with our invention in its preferred form, a-direct current is passed through the piece'to be tested and a pair of saturation type flux-responsive units is carried along the test piece. The flux-responsive units are spaced apart along the length of the test piece so as to be acted upon diiferentially in case of non-uniformities in the magnetic field surrounding the test piece caused by defects or flaws therein. The flux-responsive units may be of the type employed in the flux-measuring device illustrated in Fig. 3 of a copending application of Cramer W. La Pierre, Serial No. 13,273, filed March 27, 1935 and assigned to the same assignee as th present application. Means actuated by the flux-responsive units are provided for producing a mark whenever a defect in the rail is located. The mark may be made directly upon the rail or upon a record chart representing distances along the rail.

The features of our invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. A better understanding of our invention may be obtained from the following description taken in connection with the accompanying drawing which is a perspective view representing schematically one embodiment of our invention.

In the drawing, the piece to be tested is represented by a portion of a rail i such as used in railway tracks. It will be understood that the testing apparatus is preferably carried by a car arranged to run along a track being tested. However, our invention does not reside in any features of the test car and we have, therefore, not illustrated the car in the drawing.

A direct-current generator [I2 is provided for passing a current longitudinally through successive portions of the rail as they are tested. Brushes it connected to the generator [I2 may be provided to make the necessary contact with the rail for causing the current from the generator l2 to flow therethrough. A pair of fluxresponsive units it and it is so mounted that the units may be carried alongjust above the surface of the rail and spaced apart a suitable distance, for example, about 3 inches measured Serial No. 27,564

in a longitudinal direction with respect to the rail.

The flux-responsive units It and i5 comprise laminated three-legged cores of iron or other suitable magnetic material. The cores comprise the center legs l6 and ll and the pairs of outer legs l8 and i9 and 2t and 2t. Magnetizing windings 22, 23, 2t, and are mounted on the outer legs it, it, 20, and 20, respectively. A source of alternating current 26 is provided to which the magnetizing windings 23 to 25 are connected in series.

The connections are such that the windings 22 and 23 of the unit it tend to produce opposing magnetomotive forces in the center leg l6 and likewise the windings 2t and 25 of the unit It tend to produce opposing magnetomotive forces in the center leg ll. Detecting windings 21F and 28 are mounted upon the center legs l6 and ill of units it and i5, respectively, and are connected in series-opposition. Preferably, an amplifier 29, which may be of the vacuum tube type, for example, is provided and the windings 217 and 28 are connected to input terminals of the amplifier 29.

A suitable marking device, such as a stripchart recorder 30 or a paint spray gun M, is connected to output terminals of the amplifier. 29. The recorder 30 may be acurve-drawing instrument of any desired type having a pen or a stylus 22 producing a record curve 32 on a strip chart at. It will be understood that the strip chart 3A is advanced at a rate corresponding to the rate at which the flux-responsive units it and it are carried along the rail HI and this may be accomplished, if desired, by means of gearing driven by a wheel traveling along a track it.

The spray gun 3i may be any suitable type of paint gun known in the art that is capable of projecting a spray of paint 35 upon the rail it whenever a suitable valve therein is released by current produced by the amplifier 29. The paint gun til does not constitute a part of our invention and is, therefore, not described in detail.

The operation of the apparatus is as follows:

A current from the generator i 2 flowing through the rail in will produce a magnetic field encircling the rail and this field will be substantially uniform along the rail as long as the rail remains substantially uniform. However, in case of any flaws or defects in the rail, such as cracks or fissures, the distribution of current through the rail will be modified and, consequently, the magnetic field in the vicinity of the defect will be altered. As a result, the fluxresponsive units M and i will be subjected to different unidirectional magnetic fields when one of the units is in the vicinity of a defect in the rail. 1

The magnetic cores of the units 14 and I5, however, are also subjected to alternating magnetomotive forces by the alternating current supplied from the source 26. It will be observed that, in one of the outer legs of the core at any given instant, the unidirectional magnetic field and the magnetomotive force produced by the alternating-current winding will act in the same direction but, in the other outer leg, the magnetomotive forces will be in opposite directions. Consequently, as explained in the copending application of La Pierre mentioned above, unsymmetrical fluxes will be produced in the cores of the units l4 and I5. These unsymmetrical fiuxes will be combined in the center legs.

The components of the fluxes alternating at the fundamental frequency of the alternating current source, and the odd harmonics of these components as well, will be canceled in the middle legs of the cores owing to the fact that the alternating-current magnetizing windings of each core are connected to act oppositely with respect to the middle leg of the core. However, owing to the lack of symmetry of the flux waves caused by saturation of the core, the components of the fluxes alternating at double frequency will act cumulatively in the middle legs of the cores. Likewise, the other even harmonies will act cumulatively. Consequently, even harmonic voltages will be induced in the windings 21 and 28. i

The windings 21 and 28are connected in opposition so that, when the flux-responsive units l4 and I5 are subjected to equal unidirectional magnetomotive forces by the current flowing through the rail, there will be no response in the amplifier 29 but, when a defect occurs, the even harmonic voltages in windings 21 and 28 will be unbalanced and the amplifier 29 will be energized to cause operation of the recorder 30 or the spray gun 3|. If desired, the amplifier 29 may be tuned to the second harmonic of the alternating-current source 26 so that it will respond only to unbalanced second harmonic voltages in the windings 21 and 28, and spurious indications will not be obtained as a result of electrostatic or electromagnetic induction from the current source 26, the machinery of passing trains or nearby power lines, as the testing apparatus travels along the track being tested.

In accordance with the provisions of the patent statutes, we have described the principle of operation of our invention together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood that the apparatus shown is only illustrative and that the carried out by other means.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A rail defect locator comprising in combination, means for passing a direct current longitudinally through a rail, a pair of magnetic cores comprising saturable magnetic material, each with an inner leg and two outer legs, said cores being adapted to be spaced apart along the rail transverse thereto, a source of alternating current, windings on the outer legs of said cores connected in series to said source of alternating current, the connections of the windings of each core being such that the fluxes produced thereby tend to pass through the middle leg in opposite directions, detecting windings on the middle legs of said cores connected in series-opposition, and a current-responsive device connectcd in series with said detecting windings.

2. Magnetic test apparatus comprising in combination, means for passing a direct current through a test piece, a pair of magnetic cores comprising saturable magnetic material adapted to be brought into proximity with said'test piece, means for producing alternating magnetomotive forces in said cores acting oppositely in different parts thereof, whereby magnetic fluxes are produced unsymmetrically in said cores in response to the joint effect of said magnetomotive forces and the magnetic field produced by said direct current, detecting windings on said cores linking said unsymmetrical fluxes to induce even harmonic voltages, and a current-responsive device, said detecting windings being connected in series-opposition to said currentresponsive device.

3. Magnetic test apparatus comprising in combination, means for setting up a magnetic field in space containing a portion, at least, of a test piece, a pair of magnetic cores comprising saturable magnetic material adapted to be brought into proximity with said test piece, means for producing alternating magnetomotive forces in said cores acting oppositely in different parts thereof, whereby magnetic fluxes are produced unsymmetrically in said cores in response to the joint effect of said magnetomotive forces and said magnetic field, detecting windings on said cores linking said unsymmeinvention may be trical fluxes to induce even harmonic voltages,

and a current-responsive device, said detecting windings being connected in series-opposition to said current-responsive device.

CRAMER W. LA PIERRE. ROBERT F. EDGAR. 

